Champlain Clays Research Articles

Critical insights in laboratory shear wave velocity correlations of clays

Shear wave velocity, Vs, is an important mechanical–dynamic parameter allowing the characterization of a soil in the elastic range (γ < 10–3%). Thirty-five existing Gmax or Vs laboratory correlations were examined in this study and are grouped into different general forms based on their geotechnical properties. A database of 11 eastern Canadian clay deposits was selected and used for the critical insights. The effect of the coefficient of earth pressure at rest, K0, was also examined. A range of variation for each general form of correlation was determined to take the plasticity index and void ratio values of investigated sites into account. The analysis shows a significant scatter in Vs1 values predicted by existing correlations and raises questions on the applicability of these correlations, especially for eastern Canadian clays. New correlations are proposed for Champlain clays based on laboratory measurement of Vs using the piezoelectric ring-actuator technique, P-RAT, incorporated in consolidation cells. An analysis of P-RAT results reveals the sample disturbance effect and suggests an approach to correct the effect of disturbance on laboratory Vs measurements. The applicability of the proposed correlations, including the disturbance correction, is validated by comparison with in situ measurements using multi-modal analysis of surface waves (MMASW).

Physical modeling and arbitrary Lagrangian\u2013Eulerian finite element analysis of indentation of a sensitive clay by a flat-ended axisymmetrical indenter

Because indentation tests which are used in several engineering fields allow obtaining material strength parameters in a fast, reliable and reproducible manner, the present study was initiated with the aim of finding out whether such tests could also be used in geotechnical engineering. Experimental results are obtained from undrained indentation tests performed with a rigid flat-tipped, cylindrical indenter on Champlain clay specimens in order to deduce values of elastic moduli and yield stresses. These values are compared to those deduced from unconfined compression tests. Results of an Arbitrary Lagrangian–Eulerian (ALE) based finite element analysis that simulates such test are also presented. It is assumed that the clay behaves as a linear-elastic, perfectly plastic material obeying von-Mises yield criterion. A frictionless contact interface is chosen to realistically model interactions on the indenter-clay, clay-platen and clay-ring interfaces. The paper presents distributions of contact pressures beneath the indenter and along lateral and lower boundaries. Typical contours of von Mises deviator stress and equivalent plastic strain corresponding to different indentation depths in the clay specimen are presented. It is also shown that the presence of hairline cracks on the clay along the perimeter of the indenter and the limited thickness of the sample affect the deduced values of Young’s modulus and yield stress.

Stiffness– and damping–strain curves of sensitive Champlain clays through experimental and analytical approaches

Stiffness degradation, G/G0, curves of Champlain clay at St-Adelphe, Quebec, and the associated variation of its damping ratio with shear strain are constructed in this study using the new combined triaxial simple shear (TxSS) apparatus. The apparatus offers the ability to obtain the stiffness (G/G0) and damping ratio of soils over a wide strain spectrum from 0.001% to 10%. The value of the small-strain stiffness of the tested clay is further confirmed through another series of piezoelectric ring-actuator technique (P-RAT) tests. Although, the stiffness degradation curve of the tested clay follows to some extent traditional curves suggested in the literature, the examined Champlain clay exhibits a different trend with respect to hysteresis damping, especially at large strains (>1%), and available analytical models could not successfully predict the damping behavior of the Champlain clay at such a strain level. A new constitutive model is therefore presented as a modification of the original Sig4 model considering the pore-water pressure built up with shear strain. Stiffness degradation and damping ratio versus shear strain curves of Champlain clays estimated using the proposed soil model are similar to their experimentally determined counterparts even at large shear strains where other models tend to misjudge the damping behavior of the clay.

Pore pressure response to barometric pressure change in Champlain clay: Prediction of the clay elastic properties

Champlain Sea clay deposits play a crucial role in limiting contaminant migration to underlying aquifers in the Saint Lawrence River Valley. Champlain Sea clays are well known as being prone to landslide and sample disturbance. Estimation of their elastic properties using their in situ loading efficiency would provide mechanical properties for the soil dynamic analyses and immediate settlement calculations encountered in geotechnical projects. Determination of loading efficiency can be envisioned as a very small strain test. In this paper we describe a detailed monitoring program for 10 vibrating wire piezometers installed within sealed boreholes on 5 study sites near Montreal in Quebec, Canada. The pore pressure response to barometric pressure variation was analyzed with three methods: linear regression, visual inspection, and multiple regression, which gave loading efficiencies between 0.7 and 0.95. These values were then used to estimate the elastic properties of the clay formation. Vertical compressibility and specific storage on the order of 1×10−6kPa−1 and 1×10−5m−1 were respectively obtained for most of the monitoring sites. A comparison of compressibility values derived from the in situ loading efficiency method, with those obtained with pressuremeter, oedometer, and pulse tests confirmed that clay compressibility is strain dependent. The pore pressures measured on the study sites have been corrected by applying the multiple regression and visual inspection methods. For most piezometers, both methods provided nearly identical results. However, for deep piezometers, the multiple regression method provided smoother pore pressure time series than the visual inspection method. The vertical hydraulic gradient obtained with corrected pressure data was shown to change significantly on some test sites during the monitoring period.

Nouvelle Autoroute 30: a Champlain clay crust earthworks case study

The Champlain Sea Basin in eastern Canada is known for its sensitive clay and associated engineering problems through this much-developed area along the St Lawrence River. Geologically, the surface of the Champlain clay has been subjected to desiccation, frost action, and weathering. This has resulted in the reduction of the water content and sensitivity of the surficial crust layer of this very wet clay deposit sufficiently to enable it to be used as an earthworks material. However, the material is still much wetter than its optimum moisture content. By co-operative value engineering, the team on the Nouvelle Autoroute 30 project in Montréal, Quebec, investigated and achieved moisture content and degree of compaction derogations to the Ministry of Transport, Quebec specification. This allowed the successful construction of many low and high road embankments using an unprecedented 2.3 × 106 m3 of this weathered Champlain clay crust material. This paper describes how the design and construction issues associated with using this material for earthworks were evaluated and addressed.

Performance of a reinforced embankment on a sensitive Champlain clay deposit

An existing elastoviscoplastic constitutive model is modified using concepts of the state-dependent fluidity parameters and the damage law, to incorporate the effect of soil structure and its destructuration. The model is employed to simulate the performance of a well-documented case study of the reinforced test embankment constructed over a sensitive Champlain clay deposit at Saint Alban, Quebec. The finite element calculations, using both the original (nonstructured) and modified (structured) elastoviscoplastic soil models, are compared with the observed field data from a test embankment brought to failure. The results from the structured elastoviscoplastic soil model show better agreements with the field data when compared with those analyzed using the nonstructured elastoviscoplastic soil model. The modified model captures many features of the reinforced embankment behaviour, such as vertical settlement, excess pore-water pressure responses, and reinforcement force. However, they also reveal the fact that another important characteristic of the natural clay deposit — anisotropy — needs to be considered to provide an adequate prediction of horizontal deformations. The role of geosynthetic reinforcement and its viscosity on short-term responses of the reinforced embankment examined in this study is also discussed

A microstructure approach to the sensitivity and compressibility of some Eastern Canada sensitive clays

Investigation of micro–macro relationships in soils most often concerns granular soils in which both the elemental unit (the grain) and the physical laws governing inter-grain interactions appear to be better known. The situation is different for clays because the elementary unit and the inter-unit interactions at the micro-scale are more difficult to characterise. In fine-grained soils, it has been shown that an intermediate level, corresponding to the way clay and fine-grained particles are arranged together, had to be considered so as to link microscopic features to macroscopic behaviour. An investigation of the change in microstructure during compression carried out some time ago on a sensitive clay from Canada demonstrated that studying the changes in pore size distribution provides a satisfactory description of microstructure changes during compression. The analysis is applied here to six other sensitive clays. First, a careful examination of the intact and remoulded microstructure is conducted in order to understand better the relationship between microstructure and sensitivity. Second, an interesting correlation between the compressibility coefficient and the slope of the cumulative pore size distribution curve is observed in Champlain clays. This confirms the analysis conducted that compression in loose, low-plasticity soils can be attributed to the progressive and ordered collapse of pores, starting from the largest existing ones and progressively affecting smaller and smaller pores. A conclusion drawn from this work is that a micro–macro analysis in terms of changes of a rigid fragile porous matrix appears to be more relevant than a standard analysis based on the behaviour of individual grains, where the grains are taken to be the relevant elemental microstructure unit (a unit difficult to identify in natural clay soils). Also, further insight is provided for the interpretation of microstructure effects through comparing the compression curves of intact soil samples to those of remoulded samples.

Design of Foundations on Sensitive Champlain Clay Subjected to Cyclic Loading

Sensitive clay subjected to cyclic loading may experience gradual loss of its shear strength, which may lead to liquefaction. Foundations built on this clay would suffer extensive settlement and significant loss of bearing capacity or perhaps catastrophic failure. This paper presents an experimental investigation on sensitive (Champlain) clay obtained from the city of Rigaud, Quebec (Canada). Consolidation tests, static and cyclic undrained and drained triaxial tests were performed on representative samples of this clay. The objective of this investigation was to examine the influence of the physical and mechanical parameters, which govern the shear strength of sensitive clay subjected to cyclic loading. Based on the results of the present investigation and those available in the literature, it can be reported herein that the undrained response is the most critical for these foundations; furthermore, the preconsolidation pressure is considered as an important parameter in establishing the shear strength of sensitive clay. A design procedure is developed to determine the safe zone for the undrained and drained responses, within which a combination of the cyclic deviator stress and the number of cycles for a given soil/loading/site conditions can achieve a quasielastic resilient state without reaching failure. The proposed design procedure is applicable to all regions around the world, where sensitive clays can be found. Furthermore, this procedure can be adopted to examine the conditions of existing foundations built on sensitive clay at any time during its lifespan.

Stress-path dependent behavior of a weathered clay crust

Triaxial compression and oedometer consolidation tests are commonly performed to evaluate the strength and deformation behavior of soils. However, in the field, the stress paths imposed by various engineering works may deviate from the stress paths conventionally used in laboratory tests. Moreover, the stress-paths followed by different soil elements under a foundation are different. To obtain representative soil parameters, the laboratory stress path should be similar to that followed in the field. In this study, a significant number of stress-path triaxial tests, with stress probes in various directions, have been conducted to study the stress-path dependent behavior of an overconsolidated weathered crust of Champlain clay in Eastern Ontario. Both undrained and drained tests have been conducted for samples isotropically consolidated to the in situ vertical stress and anisotropically consolidated to in situ state of stress. The yield locus of the clay crust has been defined. It has been observed that the strength-deformation and yielding behavior of this weathered clay crust highly depends on the stress-path as well as on the in situ stress history.

Assessment of self-boring pressuremeter tests in sensitive clay

The present paper analyzes field test results obtained by means of the Cambridge self-boring pressuremeter (SBPM) in a sensitive Champlain clay of Quebec. It is shown that, although the undrained shear strengths deduced from the SBPM tests are higher than the values obtained with the field vane, the observed discrepancy is reduced by taking into account progressive failure effects. It is not the SBPM test that overestimates the undrained shear strength, but rather the vane test that underestimates it in this sensitive clay. Total and effective field stress paths are inferred from the SBPM tests, and it is shown that the effective stress paths approach the tension zone of the Mohr–Coulomb failure diagram before heading towards the large-strain failure envelope of the clay. The pressuremeter interpretation has been thoroughly worked through for various uncertainties like undrained test conditions, plane-strain conditions, and disturbance, basing the final judgment on a comparison of the effective stress adjacent to the probe with that inferred from laboratory testing. It is also shown that the pore-water pressure, which is generated at the wall of the cavity during the plastic phase of the expansion, is practically equivalent to the increase in total radial pressure. The iterative forward modelling (IFM) technique is used to obtain linearly elastic – perfectly plastic soil parameters by constraining the fit to match the initial horizontal pressure.Key words: self-boring pressuremeter, sensitive clay, stress paths, strain rate, progressive failure, pore pressures, vane tests.

Tension tests on wedge-piles in sensitive clays

The wedge-pile, a piling system in which a pile is expanded once jacked or driven into the ground, was developed at Imperial College, England. The expansion of the pile generates an increase in bearing capacity of the piling system which is closely related to the soil type. In the present study, the wedge-pile system has been tested in three sensitive Champlain clay deposits of different overconsolidation ratios. The piles were tested in tension and the test results show that in such deposits the average increase in pull-out capacity is about 30%, which is relatively small. An approach for predicting the enhancement in pull-out capacity using a closed-end self-boring pressuremeter is proposed. Simulation of the wedge-pile before and after its expansion was performed using this tool and showed that the increase in radial effective stress due to pressuremeter expansion appears to be in good agreement with the increase in the friction mobilized during pile tests.Key words: sensitive clay, wedge-pile, traction test, skin friction, pressuremeter, holding test.

DIRECT SHEAR TEST RESULTS ON ARIAKE, BOTHKENNAR, CHAMPLAIN AND DRAMMEN CLAYS

DIRECT SHEAR TEST RESULTS ON ARIAKE, BOTHKENNAR, CHAMPLAIN AND DRAMMEN CLAYS

Laboratory and field determinations of small-strain shear modulus for a structured Champlain clay: Discussion

Laboratory and field determinations of small-strain shear modulus for a structured Champlain clay: Discussion

Laboratory and field determinations of small-strain shear modulus for a structured Champlain clay: Reply

Laboratory and field determinations of small-strain shear modulus for a structured Champlain clay: Reply

Laboratory and field determinations of small-strain shear modulus for a structured Champlain clay : G. Lefebvre, D. Leboeuf, M. E. Rahhal, A. Lacroix, J. Warde & K. H. Stokoe II, Canadian Geotechnical Journal, 31(1), 1994, pp 61–70

Laboratory and field determinations of small-strain shear modulus for a structured Champlain clay : G. Lefebvre, D. Leboeuf, M. E. Rahhal, A. Lacroix, J. Warde & K. H. Stokoe II, Canadian Geotechnical Journal, 31(1), 1994, pp 61–70

Laboratory and field determinations of small-strain shear modulus for a structured Champlain clay

Values of small-strain shear modulus Gmax, for a Champlain Sea clay deposit were obtained both under an embankment built 18 years ago, and outside of the area influenced by this embankment. The small-strain shear moduli Gmax were measured in the laboratory by using resonant column tests and in the field by spectral analysis of surface waves. In addition to verifying the two methods, comparison of the in situ and laboratory values allowed evaluation of the influence of the sampling and the need to correct the laboratory values to account for the age of the deposit. The test program also made it possible to verify the influence of the deposit's consolidation and the existing models predicting small-strain shear moduli in clay deposits. Key words : shear modulus, shear-wave velocity, resonant column, in situ test, surface waves, soft clay.

Foundation problems in Champlain clays during droughts. II. Case histories

This paper presents the results of a 3 year monitoring program of the volumetric water content in two clay deposits on Montréal Island. The water content was monitored by means of a neutron depth moisture probe, which was lowered down in a series of 3–6 m deep, permanently installed, aluminium access tubes. These tubes are located at various distances from deep-rooted trees on two experimental sites. On the first site, a two-storey reinforced concrete building, surrounded by four rows of 15–20 m high silver maples, has suffered a differential settlement of over 150 mm. On the second site, a three-storey apartment block, surrounded on two sides by a row of 5–10 m high maples, has suffered a differential settlement of about 50 mm. The paper analyses the volumetric water content variations and compares them with both the rainfall deficits calculated for the period of observation and the elevation profiles of the building foundations. In addition, a comparison is made between the observed damages and a classification proposed by the Building Research Establishment of England. Key words : volumetric water content, trees, settlement, distortions, clay deposits, seasonal variations, damages.

Evaluating Ko in Champlain clays with hydraulic fracture tests : Lefebvre, G; Bozozuk, M; Philibert, A; Hornych, P Can Geotech JV28, N3, June 1991, P365–377

Evaluating Ko in Champlain clays with hydraulic fracture tests : Lefebvre, G; Bozozuk, M; Philibert, A; Hornych, P Can Geotech JV28, N3, June 1991, P365–377

Evaluating Ko in Champlain clays with hydraulic fracture tests

Hydraulic fracture tests using piezometer tips 10–500 mm long were performed in Champlain clays at five different sites with overconsolidation ratios (OCR) varying from 1.6 to 4.8. Before the test, the piezometer fluid was replaced by a methylene blue solution (10 g/L) to dye the fissures resulting from the test. After the hydraulic fracture, the soil around the piezometer tips was recovered by means of a large-diameter sampler. For 300 and 500 mm long piezometers, the fissure pattern was radial and vertical, even in deposits with an OCR above unity, confirming that hydraulic fracturing is related to the total stress acting on the cavity walls. The results for the five sites define for the Champlain clay deposits a Ko–OCR relationship that gives higher Ko values than generally proposed in the literature. Key words: hydraulic fracture, piezometer tip, sensitive clay, fissure, stress ratio Ko, overconsolidation.

Foundation problems in Champlain clays during droughts. I: rainfall deficits in Montreal (1930–1988) : Silvestri, V; Soulie, M; Lafleur, J; Sarkis, G; Bekkouche, N Can Geotech JV27, N3, June 1990, P285–293

Foundation problems in Champlain clays during droughts. I: rainfall deficits in Montreal (1930–1988) : Silvestri, V; Soulie, M; Lafleur, J; Sarkis, G; Bekkouche, N Can Geotech JV27, N3, June 1990, P285–293